Vehicles with an internal combustion engine may be fitted with fuel vapor recovery systems wherein vaporized hydrocarbons (HCs) released from a fuel tank are captured and stored in a fuel vapor canister containing a quantity of fuel-absorbing material such as activated charcoal. Eventually, the fuel vapor canister may become filled with an amount of fuel vapor. The fuel canister may be cleared of fuel vapor by way of a purging operation. A fuel vapor purging operation may include opening a purge valve to introduce the fuel vapor into the cylinder(s) of the internal combustion engine for combustion so that fuel economy may be maintained and fuel vapor emissions may be reduced.
Activated charcoal has been found to be a suitable fuel vapor absorbing material to be used in such a canister device because of its extremely porous structure and very large surface area to weight ratio. However, this porous structure can be blocked and lose its efficiency when coated with liquid fuel. This may occur if, for example, during refueling a pump operator adds fuel after an initial automatic shut-off. For instance, the maximum fill level for liquid fuel within a fuel tank is typically controlled by a mechanical shut-off valve that closes responsive to the level of liquid fuel in the tank. When this valve (frequently termed a fill limit vent valve) closes, pressure inside the tank increases thus causing liquid fuel to back up in a fill tube which actuates an automatic shut-off of a vehicle refueling pump nozzle, thus terminating the flow of fuel into the fuel tank. In an attempt to maximize the amount of fuel pumped into the tank, a pump operator may dispense additional fuel after an automatic shutoff, in what is commonly referred to as “trickle-filling”. If, as a result of trickle-filling the fuel tank, liquid has entered the fuel vapor recovery lines and a purge cycle is commanded at the next engine start, the liquid can get sucked into the canister and corrupt the activated carbon. This may decrease the efficiency of the canister and lead to increased HC emissions. Additionally, if liquid fuel in the canister or purge line is purged to the intake, a reduction of engine power and increase in combustion emissions may result from an extremely low air-fuel ratio (A/F). Overfilling the fuel tank may also impact a distance to empty calculation, and may lead to increased levels of evaporative emissions as the fuel vapor canister may not be able to adsorb fuel vapors in excess of 100% fuel fill level during a refueling event.
As the fuel limit vent valve is a passive mechanical valve, the FLVV reaction time must be designed, validated, and tested properly which involves time and resources. For example, mechanical FLVVs are typically designed based on the shape and size of the fuel tank in which they will operate, and as such one mechanical FLVV may not be suitable for use in a different fuel tank. Additionally, the fill level in a fuel tank may vary from one refueling event to another when mechanical FLVVs are relied upon for shutting off refueling dispensers, as repeatability between refueling events may vary, and over time the FLVV may develop hysteresis, stiction, and may not function per design. Furthermore, mechanical FLVVs may not prevent extensive trickle-filling after an initial automatic shutoff. The inventors herein have recognized these issues.
Toward this end, U.S. Pat. No. 7,347,191B2 teaches an electrically operated vent valve (EOVV) configured such that in an open position fuel vapor may be vented from a fuel tank, and wherein in a closed position fluid flow is restricted. The EOVV may be actuated by a controller, responsive to a signal to close the EOVV when the fuel tank is full, or nearly so, thus terminating venting from the fuel tank. As such, since fuel vapor cannot be displaced from the fuel tank with the EOVV closed, pressure within the fuel tank may build resulting in the triggering of an automatic shutoff of a refueling dispenser. U.S. Pat. No. 7,347,191B2 further teaches that additional fuel (e.g., “rounding up” or “trickle-fill) may be permitted to be added to the fuel tank after a certain interval of time subsequent to an initial automatic shutoff event, by commanding the EOVV open, and subsequently closing the EOVV after a preprogrammed interval, for example. However, the inventors herein have recognized potential issues with such a method. For example, permitting additional fuel to be added subsequent to an initial autocratic shutoff, wherein control over the additional refueling relies on a subsequent pressure build induced by adding fuel to the fuel tank in order to repeatedly shut off the refueling dispenser, may in some cases result in liquid fuel entering the fuel vapor recovery lines. Furthermore, even if the EOVV were commanded closed and maintained closed to prevent any further addition of fuel to the fuel tank, maintaining the pressure in the tank above a threshold that may prevent any subsequent addition of fuel may be problematic without active control over the pressure in the fuel tank.
Thus, the inventors herein have developed systems and methods to at least partially address the above issues. In one example, a method is provided comprising, storing pressure in a vessel external to a fuel tank that supplies fuel to a vehicle engine; and selectively coupling the vessel to the fuel tank to pressurize the fuel tank to a predetermined pressure threshold responsive to an indication that a fuel level in the fuel tank has reached a predetermined fuel fill level during a refueling event.
As one example, the predetermined pressure threshold induces an automatic shutoff of a refueling dispenser, the refueling dispenser supplying fuel to the fuel tank during the refueling event. In this way, automatic shutoffs of refueling dispenser pumps may be rapidly and reliably induced, thus preventing fuel tank overfilling, prolonging the lifetime of fuel vapor storage canisters, and reducing undesired evaporative emissions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
The inventors herein have recognized the above-identified issues and potential approaches, along with the corresponding advantages, if any.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.